LC50 and LC90 values from these analyses are presented in Table 1. Overall, zeta-cypermethrin exhibited the lowest LC50, followed by spinosad and malathion, respectively. However, when comparing LC90s, spinosad exhibited the lowest value of the three materials tested. These results differ from previous studies which found that, at the adult stage, spinosad lethal concentration values are greater than both malathion and zeta-cypermethrin. Together, these studies suggest that the relative efficacy of insecticides may differ across life stages or as a result of the different exposure routes they experience . This pattern of larval susceptibility does not appear to be caused by the different solvents used to dilute our insecticides, as the number of flies that emerged from ddH2O- and acetone-treated bottles was similar. In all cases, larval LC90 values fell far below the maximum caneberry field application rate of each material. For malathion, the maximum label rate is 139 times greater than the larval LC90 found here; the spinosad label rate is 24 times higher than the larval LC90; and the zeta-cypermethrin label rate is 29 times higher than the larval LC90. However, the concentrations experienced by larvae in the field, within infested fruit, are likely significantly lower than the field application rates. Indeed, a recent study by Andika et al showed that treating D. suzukii infested cherries with the label rate of various insecticides significantly reduced, but did not eliminate, larval survival and adult emergence in most instances. For zeta-cypermethrin, specifically, plant pot with drainage residue concentrations within the fruit were measured across two years, and high variability was observed.

In 2018, an average concentration of 3.7 ppm was detected at the subsurface level, whereas 2017 results detected no zetacypermethrin residue within the fruit. These findings suggest significant overlap in the range of concentrations tested here and those experienced by D. suzukii larvae in the field.The change in adult susceptibility to spinosad due to larval selection was assessed by performing dose-response analysis on Watsonville D. suzukii before and after imposing five generations of selection. Prior to implementing the larval selection protocol, male and female WAT adults exhibited significantly higher LC50 values than their same-sex counterparts from the susceptible Wolfskill population . Specifically, we observed RRs of 4.9 and 6.8 for WAT males and females, respectively . These values are similar to those reported by Gress and Zalom which tested the same field populations in fall of 2017 and found RRs of 4.3 for males and 5.2 for females. Following larval selection, WAT-S5 males exhibited LC50s 75% higher than pre-selection WAT males , similar to the 86% increase observed using the adult selection method. In contrast, female resistance increased more rapidly with larval selection than with adult selection . As a result, WAT-S5 RRs increased to 12.6 for males and 14.4 for females when compared to the susceptible strain. It is currently unclear what accounts for the sex-specific response patterns observed in these studies, and future work should investigate this question in greater detail. When comparing adult mortality in the Wolfskill population during the first and second assessment periods, we found no significant difference in female susceptibility . Males, however, exhibited a marginally significant decline in LC50 during the second assessment . This finding raises the possibility that laboratory conditions or other sources of error could have increased the potency of spinosad residues during the second assessment period. If true, our results may underestimate the real evolutionary potential for resistance to increase in the near-term.

Nevertheless, this study provides the first evidence that larval selection can be used as an effective tool for performing resistance risk assessments in D. suzukii and is capable of increasing both larval and adult tolerance to the target AI. In a previous study, Smirle et al attempted to select for malathion resistance in D. suzukii from British Columbia, Canada using a different larval selection protocol developed for D. melanogaster, but the concentration of malathion used had no impact on D. suzukii larval survival or eclosion success. Perhaps unsurprisingly, no malathion resistance was observed despite 30 generations of exposure. By identifying lethal concentrations of commonly used insecticides for susceptible D. suzukii larvae, this study provides a valuable resource for researchers looking to perform resistance monitoring or risk assessments on field populations of interest. We expect that this information will become increasingly more important as the widespread use of these critical insecticides results in the loss of susceptibility throughout North America, South America and Europe. To this point, a recent study by Mishra et al found that D. suzukii collected from commercial blueberry fields in Georgia exhibited a 3-fold increase in tolerance to malathion, spinosad, and zeta-cypermethrin relative to flies from an untreated location, indicating that resistance could soon emerge in other locations. The larval bio-assay, whether used for resistance monitoring or selection studies, also offers several advantages over the adult glass vial approach that makes it appealing across many experimental contexts. First, implementing this protocol requires little time, effort or cost investment beyond what is already required for standard D. suzukii colony maintenance. In contrast, the glass vial approach used for adults requires 1) purchasing large numbers of glass scintillation vials, 2) rolling treated vials throughout the drying process to help ensure residues are evenly distributed, and 3) manually loading adult flies into each vial to perform the bio-assay.

The loading process can be performed either using CO2 to anaesthetize the flies or by gently aspirating the adults into the vial, and both methods have the potential to harm or kill the flies in the process. Additionally, 4) adult mortality assessments can be time-consuming and require subjective assessments of how to classify individuals at varying stages of moribundity. With larval bio-assays, survival can easily and objectively be estimated by counting the number of adults to emerge from treated and untreated bottles.Finally, because each adult female is capable of laying multiple eggs per day, a fraction of the number of adult D. suzukii are needed to conduct resistance monitoring and risk assessment studies with the larval protocol. For example, using the adult selection method adopted by Gress and Zalom if a group of 100 female D. suzukii were exposed to their LC90 concentration, on average, 10 survivor females would remain to produce the subsequent generation. In contrast, if the same 100 females were split among 5 bottles and the larval selection method was implemented using the LC90, our results indicate that, on average, more than 30 survivor adults would emerge. Moreover, because the larval bio-assay does not require killing the parental females, these flies can continue to produce new progeny, thus drastically expanding the number of potential offspring. Although we did not measure the extent to which oviposition rate or larval susceptibility changes with maternal age, previous work has shown that female reproductive output remains high for up to 90 days post-eclosion when maintained on artificial cornmeal diet. Together, these findings indicate that larval bio-assays are a simple, cost-effective approach for measuring the current state of insecticide resistance in field populations as well as the potential for greater resistance to develop. Greater effort to monitor these trends in D. suzukii field populations is needed to ensure that appropriate resistance management actions can be implemented when early susceptibility loss is detected.The indigenous cultures and communities of North America are studied in many academic disciplines, pots with drainage holes geography among them. The number of geographers who work in this area is small compared to the figures that emerge from such departments as anthropology, history, or literature, mainly because geography itself is a small discipline. A surprisingly wide range of topics, methods,epistemological stances, and regional emphases are represented in recent geographical literature nonetheless. Our purpose here is to summarize the published books and journal articles written about North American Indian and Inuit geographies during the past ten years, following a brief look at earlier work. We do so to raise awareness of this diverse and somewhat diffuse literature, and to make it more accessible to readers of this journal. Geography may be described as the study of the earth as the home of humans, a perspective on the world that includes anything occurring on the surface of the earth that has a spatial or locational aspect. With such a broad purview, geographers may contemplate their subject as an earth or life science, a social science, or as one of the humanities, depending on the particular questions they ask.

The citations included in this article point to sources representing each of these perspectives, although the social science and humanities orientations common to the study of human geography, as opposed to physical geography, are most prominent. This breadth also means that geographers often are familiar with the ideas, methods, and information coming from other academic and non-academic sources, and frequently recast them in terms of space, place, or human-environment relationships. We recognize that many people, not just academically trained geographers, work within the geography realm. In fact, some of the best work comes from people beyond our discipline, including anthropologists, folklorists, historians, planners, and others who care about the environmental, cultural, social, political, or economic geographies of life on earth. Notably, this also includes Native writers whose ideas sometimes find their way into the geographers’ writings. Although most of the references listed here emerge from within our own discipline, this review also recognizes the valuable geographical studies and ideas drawn from these other literate sources. Other geographers not inclined toward determinism tended to see historical and cultural processes as more important, and demonstrated their argument in part by pointing to ecological zones, such as the high desert plateaus of the US Southwest, where human response and adaptation had taken quite different paths, such as has occurred between the Navajo and Hopi. By no means did they rule out the possibility of environmental influence, but they were highly skeptical of single monolithic causes, preferring to see environmental conditions as offering a broad range of possibilities within which humans could respond in different ways. The most influential geographer to emerge in this historicist-possibilist critique of environmental determinism was Carl Sauer. More than anyone else, Sauer was responsible for the development of American cultural geography and the idea of a cultural landscape, or the natural landscape as transformed through human agency, where ways of living and thinking are visibly expressed on the land. Both developments are associated with the department of geography at the University of California, Berkeley, where Sauer worked from 1923 to 1975. It is in the work of Sauer and his students, or what came to be called “Berkeley cultural geography,” that studies of American Indian geographies began to emerge.5 At Berkeley, Sauer and his students were in frequent contact with noted anthropologists Alfred Kroeber and Robert Lowie, both of whom were students of Franz Boas. Like Sauer, Boas was originally trained in German geography and was critical of deterministic, environmentalist models of cultural development. As an antidote to overly general environmental theories of Indian cultural genesis, Boas and his students sought to illuminate the full complexity of Indian life through numerous empirical studies. Many addressed geographical topics, including Indian place names, environmental knowledge, and land use. These works frequently were termed ethnogeographies, empirical studies of the geographical aspects of the lives of people labeled “ethnic.” So, at Berkeley there emerged an approach to American Indian studies that grew out of both geography and anthropology more or less simultaneously, although Sauer and Kroeber had come by many of their ideas before they knew each other. In brief, work under Sauer typically involved intensive fieldwork in rural areas, historicization of the topic in libraries and archives, and a strong empiricist and anti-theoretical orientation. Most of the cultural geographies of Indian communities were written about people in Mexico, but United States examples include studies of settlement patterns, indigenous plant use, and the relations among oral traditions, traditional land use, and material culture.’ The longstanding interests of Sauer and some of his students, especially Fred Kniffen, continued well into the late twentieth century. To be sure, much has changed in the way geographers engage American Indian studies.